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Curly hair is like a box of chocolates, you never know what you're going to get. It could be super-defined one day and a frizzy concoction the next day – and it's never exactly the same from one head to another. Our mission is to equip you with the necessary tools for restoring and maintaining healthy locks and celebrating the hair you were born with! 

Physical Hair Properties Explained: Hair Density, Diameter, Ellipticity, Porosity

July 17, 2022


Verna Meachum

Learn about the importance of physical hair properties

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With extensive experience in the beauty industry, I specialize in writing for curly hair care brands, websites, and magazines.

Not only do I have curly hair, but my children, friends, family members, and even friends who are professional curly hairstylists, each with their unique curly textures.

 You get the point :) 

I also partner with a friend who holds a Ph.D. in chemistry and works as an R&D Chemist, ensuring our content is scientifically accurate and help us navigate through the misinformation around curly hair care. 

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Last Updated on April 11, 2023 by Verna Meachum

Do you know your physical hair properties? Proper hair care starts with understanding each different factor that make up your unique locks, and how to care for them accordingly.

Porosity is also an important factor, as it affects how damaged your hair is. If your hair is particularly porous, it may be more prone to damage and breakage. If you’re not sure what any of these terms mean, don’t worry! We’ll break them down for you.

By understanding these properties, you can better tailor your hair care routine to meet your specific needs.

Hair is a fundamental component of our appearance. It establishes our style, attitude, and significantly impacts how we appear to others.

Despite its importance in our lives, we often take our hair for granted – not giving much thought to how it grows or what factors influence its appearance.

Scientifically, hair is a protein appendage designed to protect our skin (scalp and body) from external factors, such as heat or mechanical stress. Its protein nature provides thermal insulation helping us maintain our body temperature.

We all have slightly different hair because we may be of different ethnic backgrounds. They’re distinct for their color, curl pattern, density, and mechanical strength. They may also differ in terms of their structure and morphology.

These factors greatly influence day to day manageability and styling of hair. They also influence our approach in choosing hair care products for our daily use.

We all know, African-American hairs are excessively curly and are different from European or Caucasian hairs.

Similarly, lightly curly or wavy hair demonstrate different style pattern. Because of their differences, they require specific haircare products for cleansing, conditioning, and styling.

Everyone needs to know their hair. The more we understand about the science of our hair, the better prepared we are to manage and style it successfully. It can guide us in choosing the products that will work best for our hair.

So, what characteristics and features should we be aware of in order to better understand our hair? What are the qualities that we must know about?

We’ll go through each basic feature and characteristics and how they can impact our haircare so that you can be an expert on your own hair in no time!

Curl type

Curl type refers to the shape of your hair’s individual strands. This can range from straight to tightly coiled.

There are several comprehensive strategies to classify hair curl patterns to discuss commonalities, product recommendations, and to understand our hair better.

One of the most widely used and accepted is the Andre Walker Hair Typing System. The hair typing system was first brought to prominence in the 1990s by celebrity hairstylist, Andre Walker, on the Oprah Winfrey Show to promote his hair care product collection.

The system classifies hair into four main categories:

  • Type 1: Straight hair
  • Type 2: Wavy hair
  • Type 3: Curly hair
  • Type 4: Kinky hair

The other dimension is defining the thickness of hair.

  • Level a is for fine hair
  • Level b for the medium hair
  • Level c is for thick hair

So, combining the two vectors, hair 2c would be wavy thick hair, so on and so forth.

It is also very possible to have more than one curl type. You might have 2b curls at the crown of your head and 3a curls in the lower half. This is perfectly normal!

Understanding curl types can help you identify the best products for your hair and how your hair responds to styling.

For example, on hair that’s naturally straight or wavy, you may opt for sprays and stylers that help hold the shape and curl, like gels and hairsprays.

On the other hand, if you have kinky hair, your strands may crave extra moisture and benefit from curl butters and leave-in conditioners.

It’s also important to note that because this system establishes expectations about hair health, it’s important not to confuse hair type and health.

How can you determine your hair curl pattern?

Take 1 to 3 hair strands from your comb and place them on a white paper or paper towel. Try to assess the curl degree and its diameter.

A zoomed-in picture may help improve the vision of observation. If your hair is between two curl types, then it is a mix of both.

How to choose a product for a particular curl pattern?

Straight hair (1a, b, or c) is very different from curly (3 a, b, or c). Their response to various to hairstyles and outdoor air moisture levels (humidity) varies significantly.

Each level has different sebum and moisture content and thus requires different hair care products.

Straight hair is generally easily weighed down. To avoid build-up and any limp down, straight hair care products need less oils and polymers.

Wavy and curly hairs (level 3) prefer volume and body and hence look for more coating products that can cover the hair shaft, hold them in a specific style for the desired time.

Kinky/Coily hairs (level 4) are dry and brittle and therefore need deep moisturizing ingredients such as natural butter (Shea, Mango, Cocoa) and natural oils. To make things clearer, when we say “moisturizing” ingredients here, we’re referring to ingredients that keep moisture in.


Hair density - low density versus high density

One of the most essential aspects to consider when styling your hair is hair density. Hair density is defined as the “number of hair fibers per unit area of scalp”.1

High hair density demonstrates a lot of hair growth in a small area, whereas low hair density indicates fewer hairs growing in the same area. Generally, if you have a lot of hair (i.e., it’s thick), you have high hair density. Conversely, if you have thin hair, you likely have low hair density.

In general, hair density is programmed by genetic make-up. In the case of hair loss, there could be various reasons for low hair density.

Among the most common are environmental issues, excessive use of hair chemical treatments, and important changes in hormones in our body.

How to measure hair density?

The exact method to determine hair density requires the help of a friend. Mark an area of the scalp and count the number of hair fibers in that area.

For example, you mark 1 cm x 1 cm area and you have 250 fibers there, the hair density would be:

Hair Density = 250/ cm2

Repeat the experiment by choosing a new area at the scalp. To conduct an experiment with three measurements, duplicate it and take an average. The higher the number, the more hair (density) there is.

What is the significance of hair density?

Hair density is crucial since a few hairs need somewhat varied hair care treatment. For example, if you have a lot of hair, you’ll want a concentrated formulation.

Due to a large number of hair fibers per unit area, they might be difficulty to comb when wet or dry. Therefore, they require formulation that is rich in polymers and emollients to facilitate detangling and provide ease of combing.

For low hair density, you need a lighter formulation. Therefore, it’s best to avoid a formulation having high molecular weight polymers, such as polyquaternium 7 & 10 or guar hydroxypropyltrimonium chloride.

Hair Ellipticity

Ellipticity defines the shape of the hair fiber. In simple words, is you hair round (circular) or elliptical (oval)?

It is defined as a variation in the diameter of the hair fiber for two axes (x-axis and y-axis).

The ratio of two axes gives us the numerical value for ellipticity. A perfectly round circle has this value 1. For the measurement of ellipticity, we need to calculate the diameter of the hair. 2-3

What does ellipticity tell us? Choosing the right product

Hair fibers with high ellipticity are more fragile and are vulnerable to break easily. In this case, kinky coily hair falls in this category and thus requires special care.

Hair care products for super curly and coily hair need more amounts of moisturizers, emollients, and detanglers. Such formulation should contain natural butter, oils, waxes, and high cationic polymers e.g. polyquaternium 7 or 10.

On the other hand, Caucasian hair with low ellipticity requires a relatively less concentrated formulation. As mentioned earlier, such hair, if applied with high levels of oils and polymers, can lead to greasy and oily hair and scalp problems.


Diameter is also known as hair breadth; it’s the width of the hair strand. Because human hair varies in diameter, this measurement is not exact. It ranges anywhere from 17 μm to 181 μm (millionths of a meter).

Diameter can be different for each individual depending on the genetic makeup. In addition, hair color is also important. Black hair is thicker than red hair. Melanin is a pigment that gives color to our hair, skin, and eyes. The higher the melanin content, the thicker the hair.

Diameter is essential to understand since it’s related to other important factors such as strength, flexibility, and elasticity.

How is hair diameter measured?

Diameter can be measured using a microscope, which is a device that measures small objects. Different ethnic groups have different diameters.

Literature review demonstrate that hair with 1a (straight fine Caucasian hair) group have an average diameter of 30 – 100 micrometer, while 4c (thick Black hair) have an average diameter of 45-120 micrometer. However, ethnic groups show the variation of diameter in the same diameter at certain points along the hair shaft.

For example, excessively curly hair have some points where the hair is quite fine and the fiber appears flattened.

These points are fragile and hair may even break, even when very little force is applied. At these points, the ratio of two axes varies and this gives the value of ellipticity as shown in the figure.

Caucasian hair has ellipticity 1.40 while excessively curly has a high of ellipticity 1.89.

Physical Hair Properties - ellipticity of hair


Hair porosity is a big challenge that we face every day. Hair is made up of keratin protein and contains millions of pores all along its shaft.

Damaged and chemically treated hair is more porous with higher pore size. Microscopically, hair porosity means it has large empty space in its cuticular layers.

Porous hair absorbs more water, chemicals and responds strongly to external humidity. They are dull with no shine and life and also are frizzy.

How is hair porosity determined?

Two different types of at-home trial approaches are “floating test” and “wet test.” Both tests do not offer accurate results nor present a true picture of hair status. Both tests give a very empirical result and suffer technical drawbacks.

For example in the floating test, hairs are placed at the water surface and if hair sink, it is porous, while if they float at the water surface, they are not porous. The technical flaw here is the wettability.

Hair may sink quickly due to the pH of water solution, temperature, or presence of salt in water. These factors influence the wettability and hence must be maintained.

Scientifically, we determine hair porosity using the weight gain method. Hair fibers are calibrated at a constant relative humidity of 65% for 24 hours. Pre-weighed hair samples are immersed in a measured amount of water having constant temperature and with no salt presence.

After a certain period, hairs are removed, dried with a towel, and centrifuged to remove surface absorbed water. The weight gain (weight before immersion and weight after) is calculated and is reported as %age porosity.4

How to take care of porous hair

Highly porous hair is damaged and require a good conditioning regimen. Shampoos for porous hair are prepared using mild surfactant blended with cationic polymers and other emollients.

Conditioners for porous hair must have humectants, proteins, emollients, and fiber softeners. Behentrimonium chloride, steartrimonium chloride, and cetrimonium chloride are the favorite choice for cationic.

Humectants are vital and glycerin is the top choice to deliver much-needed water molecules to porous hairs.

Porous hairs are difficult to comb and style. Therefore, oils are really important to provide lubricity, ease of combing, and sheen. Butter of cocoa, mango, and shea are preferred for their unique carbon chain levels.

Characteristics of Healthy Hair

Healthy hair is an important part of a person’s overall health and well-being.

Healthy hair is strong, flexible, and shiny. The individual strands are smooth and free of damage. Your hair should be able to absorb and retain moisture well.

The elasticity of your hair should allow it to return to its original shape after being stretched or pulled. If you have healthy hair, you probably don’t have to worry about it breaking, splitting, or fraying easily. Healthy hair is also well-nourished and typically free of build-up.

The hair follicles are unobstructed, allowing the strands to grow unimpeded. The scalp is clean and free of debris.

Good haircare habits, such as using gentle shampoos and conditioners and protecting the hair from heat damage, can help maintain healthy hair.

Regular trims can also prevent split ends and other forms of damage. By taking care of their hair, people can help ensure that it looks its best.


What is the difference between fine hair and thin hair?

Fine hair and thin hair may appear to be the same, but there are actually some key differences between the two. Fine hair does not imply hair is thin.

Fine hair refers to the diameter (width) of the individual strands, while thin hair refers to the density of the hair on the head.

Fine hair is also more prone to breakage, which can result in a thinner overall appearance.

In general, those with fine hair need to be gentle when styling or detangling, and use products that add body and volume.

Those with thin hair may benefit from using products that coat the strands and give the illusion of thicker, fuller hair.

Ultimately, both types of hair require special care and attention in order to maintain a healthy, lustrous appearance.

What is coarse hair?

Coarse hair is a type of hair that is thick, strong, and larger in diameter. It is often difficult to style because it does not hold onto moisture well. This can make it frizzy and difficult to manage.

People with coarse hair often have to use special conditioners and styling products to keep it under control. Coarse hair is usually dry and brittle, so it is important to use products that will hydrate and nourish it.

Deep conditioners are often essential for keeping coarse hair healthy and manageable. In general, people with coarse hair should avoid using heat-based styling tools and should focus on using products that will help to soften and moisturize the hair.

What does condition or state of hair mean?

The condition or state of your hair can tell a lot about your overall health. For example, if you have dry and brittle hair, it could be a sign that you are not getting enough essential fatty acids in your diet.

On the other hand, if your hair is oily and scalp is flaky, it could be a sign of an overactive sebaceous gland.

While these are just two examples, the condition of your hair can give you insight into your dietary habits and overall health.

If you are concerned about the condition of your hair, be sure to talk to your doctor or a qualified nutritionist. They will be able to help you determine whether or not your diet is lacking in essential nutrients.

Can your hair be dry and damaged?

Yes! Dry, damaged hair is a common problem that can be caused by a variety of factors, including over-washing, heat styling, and environmental damage.

While damaged hair may look lifeless and dull, it is actually more susceptible to breakage than healthy hair.

The best way to repair dry, damaged hair is to give it some extra TLC. Start by using a shampoo and conditioner that are specially formulated for dry hair.

In addition, try to avoid heat styling whenever possible, and use a deep conditioning treatment at least once a week.

By taking these steps, you can help restore your hair’s natural moisture balance and protect it from further damage.


1. Zviak, C., The Science of Hair Care. Taylor & Francis: 2005.
2. Syed, A. N.; T, V.; N, S. M., Hair ethnicity and ellipticity: An preliminary study. Cosmtics & Toils. 2013.
3. Robbins, C. R., Chemical and physical behavior of human hair. 4th ed.; Springer-Verlag: New York, 2002; p 311-343.
4. Syed, A. N.; Ayoub, H., Correlating porosity and tensile strength of chemically modified hair. Cosmetics and toiletries 2002, 117 (11), 57-64.


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